Environmental benefits from bioenergy production derived from sugarcane crop residues (straw) can be lost by soil organic matter depletion resulting from excessive straw removal rates from fields. Soil organic carbon stock is the core for sustaining soil health, supporting nutrient cycling, and sequestering carbon dioxide. To find out that how much sugarcane straw can be removed from the field to produce bioenergy without changes in soil C concentrations, we investigated effects of straw removal rates (total, moderate, and no removal of sugarcane straw) on soil carbon and nitrogen fractions in an Oxisol and an Ultisol in southeastern Brazil for two years. Soil C and N fractions were affected by increased rates of straw removal at the second year. In the Oxisol, total straw removal decreased labile and microbial-C by ~30% and soil C stock by 20% compared to no straw removal. No removal decreased microbial-N and total N stock by ~15% and ~20%, respectively. In the Ultisol, no straw removal resulted in increases in C stock by >10% and labile and microbial-C by ~20% related to total straw removal. Total straw removal showed more microbial-N (~10%) and total-N stock (~25%) compared to no straw removal. The moderate straw removal intensity (i.e., 8 to 10 Mg ha−1 of straw) may control the straw-C release to soil by straw decomposition. This study suggests that excessive straw removal rates should be avoided, preventing SOM depletion and consequently, soil health degradation. Moderate straw removal seems to be a promising strategy, but long-term soil C monitoring is fundamental to design more sustainable straw management and bioenergy production systems.

Yield and disease incidence were evaluated in potato (Solanum tuberosum, cv. Atlantic) after six years of cultivation in succession with corn (Zea mays, cv. 'AG 6080') under conventional tillage (CT, depth of tillage: 20 cm) or in succession with three grass species [Guinea grass (Panicum maximum, cv. Tanzânia), Palisade grass (Brachiaria brizantha, cv. Marandu) and corn] under deep tillage (DT, depth of tillage: 70 cm). Total tuber yield was higher in DT in average 36% the value obtained in CT (17.76 t/ha), with no effect of the grass species. Common scab (Streptomyces scabies) incidence was influenced by treatments, the highest (16.9%) and the lowest (9.5%) values being obtained in succession with corn and Guinea grass, respectively, both under DT. The lowest incidence of tuber greening at field (2.58%) was also recorded in Guinea DT, significantly lower than obtained in Corn CT (6.33%), possibly due to a more efficient ridging operation. Grass species showed different values of aboveground dry biomass production. Guinea grass (26.56 t/ha) was the most and Corn under CT and DT (5.72 and 5.56 t/ha, respectively, without ears) were the least productive ones. Soil density, macroporosity and resistance to penetration indices were significantly better with DT, the grass species affecting them in a minor degree. The deep tillage system is, therefore, recommended for potato cultivation regardless the grass species used for crop succession.Keywords: Solanum tuberosum, compaction, soil recuperation, crop succession. RESUMOAtributos do solo e da cultura da batata em preparo profundo de solo e sucessão com poáceas A produtividade e a incidência de doenças foram avaliadas na cultura da batata (Solanum tuberosum, cv. Atlantic) após seis anos de cultivo em sucessão com milho (Zea mays, cv. 'AG 6080') sob manejo de solo convencional (CT, profundidade da operação de preparo: 20 cm) ou em sucessão de culturas com três espécies de poácea [capim Tanzânia (Panicum maximum, cv. Tanzânia), capim Marandu (Brachiaria brizantha, cv. Marandu) e milho], sob manejo profundo de solo (DT, profundidade da operação de preparo: 70 cm). A produtividade total em tubérculos para os tratamentos em DT foi, em média, 36% maior em relação ao CT (17,76 t/ha), não havendo efeito da poácea cultivada em sucessão. A incidência de sarna comum (Streptomyces scabies) foi influenciada pelos tratamentos, sendo a mais alta (16,9%) e a mais baixa (9.5%) registradas quando milho e capim Tanzânia, respectivamente, foram utilizados como cultura em sucessão, ambos sob DT. A incidência mais baixa de esverdeamento de tubérculos em campo (2,58%) foi também obtida para sucessão com capim Tanzânia sob DT, significativamente inferior ao valor obtido em milho CT (6,33%), possivelmente devido à maior eficácia da operação de amontoa. As diferentes poáceas apresentaram valores diferentes de produção de biomassa seca de parte aérea. O capim Tanzânia (26,56 t/ha) foi a poácea mais produtiva e o milho sob CT e DT (5,72 e 5,56 t/ha, respectivamente, sem considerar as esp...

In Brazilian sugarcane (Saccharum spp.) production systems, the practice of moving harvesting residue from row to inter‐row positions (i.e., raking) has increased in response to producer concerns over the potential negative effects of sugarcane straw on crop establishment and stalk yield. Despite increasing adoption among sugarcane farmers, the impacts of straw raking practices on plant growth and yield remain unclear. A 2‐yr experiment that included both dry and wet seasons was conducted at two sites in southeastern Brazil to evaluate straw management strategy effects on plant tillering, phytomass accumulation, plant nutritional status, and stalk yield. The experiments were established at the Bom Retiro mill and the Univalem mill. Experimental treatments included raking straw to inter‐rows (raked), total straw removal (bare soil), and no straw removal (straw cover). Raked and bare soil treatments improved plant tillering but did not influence final plant population. Straw management had a slight effect on phytomass accumulation. Reduction of phytomass yield was observed from the first to the second ratoon during both seasons at both sites. At Bom Retiro, phytomass yield decreased 37% for stands established during the dry season and 19% for stands established during the wet season. At Univalem, phytomass yield decreased 20% for stands established during the dry season and 30% for stands established during the wet season. Retaining straw in the field (regardless of treatment) increased leaf tissue P content but not stalk yield. Raking straw from row to inter‐row positions at these locations in southeastern Brazil had no benefit on sugarcane yield but may result in soil compaction and higher production costs over time.

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Globally, there is increasing demand for sugarcane ethanol. To meet this demand, one way is to increase productivity by 2nd generation ethanol using sugarcane straw as feedstock. Straw removal management can change the chemical and physical soil properties. The aim of this study was to characterize the soil and assess the impacts of maintenance of different amounts of sugarcane straw on soil chemical and physical properties. Two experiments were conducted near Capivari-SP in Bom Retiro mill (BR) and close to Valparaiso-SP in Univalem mill (UV). The soil type of each experimental area was, respectively, a Rhodic Kandiudox (USDA Soil Taxonomy) and a Kanhaplic Haplustults (USDA Soil Taxonomy). The experimental design used was a randomized blocks with six treatments and four replications. The treatments were the following amounts of straw in Mg ha-1 of dry matter: BR (0, 3.4, 7.8, 13.0, 16.6, 15.6) and UV (0, 4 2, 8.7, 15.1, 18.9, 23.3). Soil chemical and physical attributes were assessed, such as content and carbon stocks, fractionation of soil organic matter, pH and soil resistance to penetration. Soil sampling was performed for the 0-10; 10-20; 20-30; 30-40; 40-50; 50-60; 60-80 and 80-100 cm layers in the soil characterization (base line) and after 1 year of effect of straw, soil was sampled at 0-5 and 0-10 cm depth. Our results showed that the soils had no significant variation in the macronutrient and C contents and C at the time of implantation of the experiments, indicating that the soil in each experimental area was homogeneous and therefore suitable for implementation of the experiment. After one year of experiment, different amounts of straw did not alter the contents of C (regardless of the assessed depth) nor the distribution of SOM fractions. Thus, we concluded that the effects of the sugarcane straw removal on soil chemical and physical attributes, if any, it should be expressed in a long-term experiment.